In a well drilling operation, joints of drill pipe generally are added one after another to the upper end of the drill string. After the well has been drilled "kelly down," that is, the length of the kelly joint, the drill string is lifted, string supporting slips are placed in position and the kelly is disengaged from the string. A new joint of pipe is then inserted between the kelly and the string.
Spare drill pipe is typically stored on a horizontal pipe rack adjacent the rig platform except for the next joint to be used which is hoisted off the pipe rack and placed in a holding tube known as a "mousehole." The mousehole allows the next joint to be held in a vertical orientation suitable for ready attachment to the drill string. Since the kelly cannot generally be moved laterally for vertical positioning over the mousehole joint, the mousehole is typically positioned in close proximity to the wellbore and slanted at an angle which facilitates threaded connection to the kelly. The kelly is then manually positioned at an angle supplementary to that of the joint and lowered so that a threaded "pin" connection of the kelly stabs into a complementary threaded "box" connection of the joint. After the threads between the kelly and new joint are made up, the joint is lifted from the mousehole and inserted into the drill string so that drilling can resume.
Due to the proximity of the mousehole to the rotary table in many rigs, the upper end of the mousehole joint is preferably positioned close to the rig floor to avoid possible interference with drilling equipment on the platform. Alternatively, the upper end of the joint in the mousehole can be held in a rotary mousehole makeup tool which is generally installed in the rig sub-floor. Thus, a situation has evolved wherein a joint once lowered into the mousehole is difficult to position for makeup by means other than by connection to the kelly.
Occasionally, the mousehole joint is not inserted directly into the string, but is handled for some additional purpose or returned to the pipe rack (e.g. following the discovery of damaged threads). However, means for retrieving the joint from the mousehole without interrupting drilling operations (i.e. by breaking the kelly from the drill string) has generally been unavailable since the box end of the joint is difficult to access as mentioned above. This can present a time consuming problem because a substitute joint cannot be retrieved from the pipe rack until after a bad joint is removed from the mousehole.
Conventional mouseholes typically use a spring at the bottom of the mousehole to absorb the shock of a joint falling into the mousehole. However, the spring does not support a smaller or pup joint which is too short to span the distance from the upper end to the bottom. Accordingly, there is a need for an apparatus which can facilitate positioning, hoisting and removal of a joint of drill pipe from a mousehole without having to cease drilling operations.